Engines may utilize recirculation of exhaust gas from the engine exhaust to the engine intake system, referred to as Exhaust Gas Recirculation (EGR), to reduce regulated emissions and/or improve fuel economy. For example, the EGR may displace fresh air to reduce peak combustion temperature, thereby reducing NOx emissions.
When the EGR temperature is too high, e.g., due to high exhaust temperature generated during high load conditions, the EGR may displace the intake air such that there is limited oxygen available for combustion. Likewise, the engine air-fuel ratio may be limited to be less than a threshold value, beyond which combustion may degrade or increased particulate matter emissions may be generated. The limited combustion air, along with the air-fuel ratio limits, can effectively restrict the maximum available fuel injection amount. The restricted fuel injection amount thus leads to reduced available engine output torque and/or power. As such, various approaches may be used in which the EGR is cooled via an EGR cooler that rejects heat to engine coolant to avoid reducing available engine output.
In a locomotive context, however, various issues may arise with the above approaches. For example, a locomotive engine duty cycle may result in excessive heat rejection to the engine coolant, thereby requiring significantly increased engine cooling system size and performance criteria. Further, the locomotive engine duty cycle may also result in significant amounts of deposit buildup, e.g., soot buildup and/or coaking, in the EGR cooler.